To determine whether B. abortus could induce memory T cells of the Th1 phenotype, mice were injected with ovalbumin (ova) in alum or ova in alum mixed with B. abortus (Ba + ova), and subsequently immunized with ova-alum alone. After the third immunization with ovaalum the mice were sacrificed and spleen cells were tested for ova-specific T-cell cytokine secretion by ELISPOT. Both IFN-γ and IL-4 spots were found, but IL-4 spots predominated in mice receiving ova-alum alone. In contrast, IFN-γ spots predominated in mice receiving BA + ova as the primary inoculum [33]. These results indicated that B. abortus as an adjuvant was capable of generating Th1- like memory cells. Mice receiving ova-alum, without prior Ba + ova developed IgE responses and allergic reactions to ova. In contrast, mice that received Ba + ova, followed by subsequent exposure to ova-alum, had suppressed levels of IgE and did not develop allergic reactions to ova. Furthermore, injections with B. abortus conjugated to ova (Ba-ova) were able to change responses to ova from Th2 to Th1. This has implications for prevention and treatment of immediate hypersensitivity reactions in susceptible individuals [33].